Denitrogenation by distillation in presence of alkali metals

ABSTRACT

LUBRICATING OIL FRACTIONS ARE TREATED WITH FINELY DIVIDED DISPERSIONS OF FREE ALKALI METALS OF ONE MICRON OR LESS TO REMOVE NON-BASIC AND WEAKLY BASIC NITROGEN COMPOUNDS AND THEREBY REDUCE THE COLOR AND INCREASE THE COLOR STABILITY OF THE OIL. FINELY DIVIDED SOODIUM IS PARTICULARLY EFFECTIVE. THE PROCES IS BEST CARRIED OUT BY DISTILLING THE OIL FROM A MIXTURE OF THE OIL AND THE METAL. HYDROFINING EITHER BEFORE OR AFTER THE ALKALI METAL TREAT OR BOTH FURTHER IMPROVES THE OIL.

United States Patent 3,649,528 DENTTROGENATION BY DISTILLATION IN PRESENCE OF ALKALI METALS Robert Kartzmark and John M. MacDonald, Sarnia,

Ontario, Canada, assignors to Esso Research and Engineering Company, Linden, NJ. No Drawing. Filed Mar. 16, 1970, Ser. No. 20,149 Int. Cl. Cg 23/02, 29/04, 31/14 US. Cl. 208-494 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to the improvement of the color and color stability of lubricating oil distillates.

Many lubricating oil distillates, such as those from Tia Juana 102 crude, contain relatively large amounts of nitrogen compounds, many of which are color precursors resulting in poor color and color stability of the distillates. It has been previously shown that it is necessary to remove at least 80 of the nitrogen compounds to obtain lube basestocks of good color and color stability. See for example the disclosures in Ser. No. 612,195, filed Jan. 27, 1967 for Kartzmark et al. and now abandoned. As taught in that application these nitrogen compounds can be removed by hydrotreating at 600-750 F. and at least 1000 p.s.i.g. The nitrogen removal may also be accomplished by conventional methods such as solvent extraction followed by hydrofining or acid treating followed by clay contacting. Mild hydrofining alone followed by vacuum distillation gives products of good color but this process is ineffective in reducing the nitrogen content and the products lack color stability. The eifective processes mentioned while marginally attractive commercially are still expensive.

distillates can be achieved by treating the oil with finely divided alkali metal dispersions consisting of particles of one micron or less in size, resulting in products of excellent color and color stability. Sodium, potassium and lithium have been found to be effective. However sodium is preferred because of its reaction efiiciency, availability and low cost. This process is most efiectively carried out by distilling the oil from its mixtures with the finely divided metal. If desired the distillation step may be preceded or followed or both by a hydrofining step.

Further study has indicated that the alkali metals remove the weakly basic and non-basic nitrogen compounds to the exclusion of the basic nitrogen compounds. Koros et al. (prepint of paper presented before Division of Petroleum Chemistry, ACS Fall Meeting, Sept. 11-15, 1967, page B-l state that strong nitrogen bases titrate in the 0-12 p range and weak bases in the 12-14 p range. It must be noted that this is an arbritrary, not an absolute, classification in that the lube nitrogen compounds are defined as basic if titratable by perchloric acid in an acetic acid-acetic anhydride medium and defined as non-basic if not titratable. Under these conditions pyridine-type compounds are defined as basic and pyrrolic types as non-basic or weakly basic. The weakly basic and non-basic compounds are the color precursors found in the oil and are the main causes of poor color and color stability.

Alkali metal treating gives both a high yield and only a moderate drop in viscosity. The process has little effect on sulfur content, and no sodium remains in the product. Nitrogen removal can be up to 83% depending on the alkali metal concentration and method of distillation.

PREFERRED EMBODIMENTS Example 1 An SAE-20 grade distillate from Tia Juana 102 crude containing 0.15 wt. percent nitrogen was hydrofined at 650 F., 0.5 v./v./hr., 800 p.s.i.g. in the presence of cobalt molybdate catalyst on A1 0 The hydrofined oil was contacted with finely divided lithium and potassium metal dispersions under specified conditions and then distilled under high vacuum conditions to overhead. The nitrogen content, Tag Robinson color, and color stability at 212 F. of the overhead product were then determined. The following data were obtained.

TABLE I.DENITROGENATION BY RERUNNING IN THE PRESENCE OF CHEMICAL REAGENTS [Blank oil: Naphthenic SAE-2O grade distillate (0.15 wt. percent nitrogen) hydrofined at 650 F., .5 v./v., 800 p.s.i.g. and rerun (ii-97%)] Nitrogen in Hydrofining Colorhold, TR, at 212 F. Treat (Wt. product By chemical plus chemical Color, Reagent percent) Conditions (Wt. percent) reagents 1 reagents 2 initial 16 hr. 48 hr. 168 hr.

Lithium 1.0 380 F./1 hr 054 49 64 16% 15% 11 9% Potassium 0. 4 240 F./1 hr .054 49 64 1 Reduction in the nitrogen content of the hydrofined rerun oil by chemical treating and Hivac distillation.

SUMMARY OF THE INVENTION It has now been found that relatively cheap and very effective reduction in color precursors in lubricating oil 2 Total reduction in the nitrogen content of the raw distillate by hydrofining plus chemical treating.

The above data show that lithium and potassium are very eifective in removing nitrogen compounds from lubricating oil distillates.

Example 2 A ra-w SEA ZO-grade distillate from Tia Juana 10-2 crude was rerun with sodium in a batch high vacuum still and the following data were obtained:

TABLE II.PYRROLIC NITROGEN COMPOUNDS RE- MOVED BY DISTILLATION OVER SODIUllI [SAE 20 grade distillate from T1 102 crude] Distillation number 1 2 Sodium treat., wt. percent on oil n 0. 4 0.7 Yield of treated oil, vol. perccnt 90 Nitrogen content, p.p.m 1, 400 490 290 Nitrogen removal, percent 65 79 Nitrogen distribution, 3 p.p.m.:

Strongly basic 4 380 325 262 Weakly basic 4 220 54 38 Non-b asic 4 800 111 N11 Color, T.R 1 5 11% 1 Raw distillate.

1 Sodium dispersed as particles of one micron or less.

3 Strongly and weakly basic nitrogen determined by perchloric acid titration in acetic anhydride. Non-basic nitrogen calculated by difleronce.

4 R. M. Koros, S. Bank, .1. E. Hofmann and M. I. Kay, Prcprints, Division of Petroleum Chemistry, A.C.S. Fall Meeting, 1967, p. B-165. Strongly basic nitrogen compounds-pyridine types. Weakly and nonbasic nitrogen compounds pyrrole types.

This example shows the very high eificiency of this method of sodium treating for removal of the deleterious non-basic and Weakly basic nitrogen compounds.

Example 3 Example 2 was repeated in a pilot plant using nitrogen as a carrier gas and a raw 20 grade distillate from Tia Juana 102 crude. The following data were obtained.

TABLE III.-VACUUM DISTILLATION OF A MIXTURE OF SAE 20 GRADE DISTILLAIE FROM T3 102 CRUDE AND SODIUM IN A PILOT PLANT CONTINUOUS UNIT Example 4 A series of raw lubricating oil distillates of different viscosity grades was rerun over sodium in a pilot plant continuous still followed by hydrofining at 600 F., 1.0 v./v./hr., and 800 p.s.i.g. The following data were obtained.

4 Example 5 Three of the raw distillates of Example 4 were hydrofined and then vacuum distilled over finely divided sodium. The following data were obtained.

TABLE V.COLOR PROPERTIES OF OILS 2, 3, AND 4 [Hydroiining followed by sodium treating] Distillate Number I 2 3 4 Sodium treat, wt. percent 0. 4 0. 4 0. 7 Oil yield, vol. percent 90 90 90 Finished oil:

Nitrogen content, wt. percent 0. 02 0.04 0.03 Total nitrogen removal, percent. 73 73 83 Color T.R +10 16% 8% Color hold at 212 F 16 hr- 19% 14 8% Color hold at 212 F., 48 hr- 9% 10 8% Color hold at 212 F 168 hr 5 7% 8% 1 Hydrofining conditions:

Distillate 2; 600 F., 1.0 LHSV, 800 p.s.i.g. Distillate 3; 650 F., 1.0 LHSV, 800 p.s.i.g. Distillate 4; 700 F., 0.5 LHSV, 800 p.s.i.g. Saybolt.

The above examples show that finely divided alkali metal dispersions of 1 micron or less are very effective in removing the slightly basic and non-basic nitrogen compounds from lubricating oils thus reducing the color precursors, decreasing color and increasing the color stability. The sulfur content is only slightly reduced.

Example 6 This example shows the importance of dispersing the sodium into particles of 1 micron or less in order to efficiently remove the nitrogen compounds from the oil. An SAE 20grade distillate from Ti-a Juana 102 crude which had been hydrofined at 650 F., 1.0 LHSV and 800 p.s.i.g. was given a 0.4 wt. percent sodium treat by two different dispersion methods. In the first method the sodium was dispersed in the oil in a high-speed Waring Blendor at 250 F. for 15 minutes. A photomicrograph of this dispersion showed that the sodium particles varied greatly with an average size of 5 to 10 microns in diameter. The sodium was allowed to react with the oil for an additional 1 hour at 400 F. and then 90% of the oil taken overhead. In the second method the sodium was dispersed in a Manton-Gaulin homogenizcr at 250 F. for 15 minutes. The distribution of sodium particle sizes was quite even and all particles were 1 micron or less in diameter. The oil was then distilled to 90% overhead. The results in the following table show the superiority of the more finely dispersed sodium for nitrogen removal.

TABLE IV.COLOR PROPERTIES OF OIL NO. 1, 2, 3, AND 4 [Sodium treating followed by hydrofining] Distillate Number 1 1 2 3 4 Sodium treat, wt. percent 0.4 0. 3 0.4 0. 7 0. 4 1. 0 0. 7 Yield, vol. percent 96 90 89 84 Inspections:

Color, T R I +12 +7 20% 16 16% 10% 10 5 Color hold, 16 hr. at 212 F., 24% 18 16 4 14% 9% 9% Color hold, 48 hr. at 212 F., 22% 18% .34 ill 9 0 Color hold, 168 hr. at 212 F., '1.R 21 10% 17% 11% 9% 8% 8% Color stability at 125 F3 T.R.:

1st cycle, 5th week 2nd cycle, 10th wcel: Daylight color stability, T.R Nitrogen, p.p.m Total nitrogen removal, percent Sulfur, wt. percent Viscosity at 100 F., SUS Viscosity at 210 F., SUS

Viscosity index Flash, COG, 300 Pour, F Gravity, API 20. 9

1 Distillates rerun over sodium in a pilot plant continuous still followed by hydrofining at 600 F., 1.0 LHSV and 800 p.s.l.g.

-' Saybolt I In this test, 500 cc. of oil were stored in a tank fabricated from 4-inch diameter rusty iron pipe and 20% was removed at the end of each week. At the end of the 5th week when 20% of the oil remained, the tank was refilled with 400 cc. of oil and the cycle repeated.

4 A 4-ounce clear glass bottle with vented stopper containing 20 cc. of oil was placed in a southern exposure sunlit window tor 47 days.

TABLE VI Distillation number 80 312 Dispersion method Average sodium particle size, microns -10 1 Oil yield, vol. percent 90 90 Nitrogen content wt percent". 0. 093 0. 041 Nitrogen removal, percent 15. 4 62. 8

l Waring blendor.

2 Homogenizer.

3 Feed oil had a nitrogen content of 0.11 wt. percent.

The nature and advantages of the present invention having thus been fully set forth and specific examples of the same given, what is claimed as new, useful, and unobvious and desired to be secured by Letters Patent is:

1. The process of reducing color and increasing color stability of lubricating oil distillates which comprises contacting a lubricating oil distillate with a finely divided alkali metal of one micron or less and separating the thus treated distillate.

2. The process of claim 1 in which the alkali metal is sodium.

3. The process of claim 2 in which the treatment with sodium is preceded by a hydrofining step.

4. The process of claim 2 in which the treatment with sodium is succeeded by a hydrofining step.

6 5. The process of claim 2 in which the treatment with sodium is both preceded and succeeded by a hydrofining step.

6. The process of claim 2 in which the distill-ate is distilled from the sodium dispersion.

References Cited UNITED STATES PATENTS 1,952,616 3/1934 Vose 208294 2,027,770 1/1936 [Fields 208294 2,042,557 6/1936 Sparks 208294 2,058,131 10/1936 Carlisle 208208 M 2,772,211 11/1956 Hawkes et al. 208-226 2,927,074 3/1960 Barger, Jr. et a1. 208208 M 2,979,548 4/1961 Clauke 208208 M FOREIGN PATENTS 903,348 8/ 1962 England. 692,448 6/ 1953 England.

DELBERT E. GANTZ, Primary Examiner G. J. CRASANAKIS, Assistant Examiner US. Cl. X.R. 

